Esterification of acetic acid with I-octanol was studied using a series of alkylammonium salts as Bronsted acidic ionic liquids. The following ionic liquids were prepared and used as catalysts and mediums in the esterification reaction; [Et3NH][HSO4], [Et3NH][H2PO4][Et3NH][BF4], [Et3NH][p-CH3C6H4SO3], [Et-2(PhCH2)NH][HSO4], [n-BU3NH][HSO4], [n-Oct(3)NH][HSO4], [Et2NH2][HSO4], [Et2NH2][H2PO4], [Et2NH2] [BF4], [i-Pr2NH2][HSO4], [EtNH3][HSO4], [EtNH3][H2PO4], and [EtNH3][BF4]. Higher acidity of the anion in the ionic liquid resulted in high yield of the ester. Yield of the ester decreased with increase in the size of the cation. There was no phase separation in the reactions where size of anion and/or cation was bigger. (c) 2007 Elsevier B.V. All rights reserved.